filename_or_file_like.py

from functools import wraps
import sys


# Goddamnit Python 2/3 differences.
str_type = str if sys.version_info[0] >= '3' else basestring


def filename_or_file_like(mode):
    """Decorator that checks if the first argument to a function is
    an instance of a string type, and opens it with the specified mode
    before calling the function.

    Example
    -------
    @filename_or_file_like('rb')
    def func_that_reads_something(f, a, b, c):
        s = f.read()
        return s
    """
    def wrapper_factory(fn):
        @wraps
        def wrapper(f, *args, **kwargs):
            # Open if it's a string
            if isinstance(f, str_type):
                with open(f, mode) as open_f:
                    return fn(open_f, *args, **kwargs)
            else:
                # Assume it's file-like
                return fn(f, *args, **kwargs)
        return wrapper
    return wrapper_factory